Intron-mediated regulation of gene expression.

Introns can significantly affect gene expression in plants and many other eukaryotes in a variety of ways. Several types of gene regulation, both positive and negative, that involve plant introns are reviewed in this chapter. Some introns contain enhancer elements or alternative promoters, while many others elevate mRNA accumulation by a different process that has been named intron-mediated enhancement (IME). The introns involved in IME must be within transcribed sequences near the start of a gene and in their natural orientation to increase expression. The intron sequences involved are still poorly defined, and the mechanism of IME remains mysterious. A model of IME is presented in which introns increase transcript elongation.